This invention relates generally to etching metal silicides and germanides in connection with semiconductor processing.
Metal silicides and germanides are conventionally somewhat difficult to etch. A robust chemistry is needed to remove the silicides or germanides. Selectively etching the silicide, while not adversely affecting surrounding components, is a problem.
One example of a situation where it is desired to etch silicide is in connection with metal gate replacement processes. In such processes, a silicon gate or, more particularly, a polysilicon gate may be removed in a selected number of instances and replaced with a metal gate.
Commonly, the polysilicon material is in contact with a metal and forms a silicide. Conventional etching may not selectively remove the silicide from the polysilicon without adversely affecting other components.
One approach to the problem is to form the metal layer over both the locations where the gate is to be removed and the locations where the gate is to remain. A hard mask may be retained over the gates that will ultimately be removed in order to prevent the formation of a silicide. However, patterning of the high dielectric constant gate oxide may be difficult without removing the hard mask. Thus, the use of a hard mask to protect the polysilicon from the silicide formation is an incomplete solution to the problem.
Thus, there is a need for better ways to facilitate the selective etching of silicides and germanides.